Athens reacted furiously after it was revealed that the British Museum had loaned one of the Elgin Marbles to Russia.

Greece’s Prime Minister, Antonis Samaras, called the move a “provocation” to his country’s people.

The long-running diplomatic row over the UK’s ownership of the ancient Greek antiquities was reignited by the loan – the first time one of the sculptures has been sent abroad since Lord Elgin brought them to London from the Parthenon more than 200 years ago.

Mr Samaras, whose government refuses to recognise the British Museum’s rights to the artworks and who has long called for them to be returned to their place of origin, said: “The Parthenon and its marbles have been looted. The sculptures are priceless.

“We Greeks are one with our history and civilisation, which cannot be broken up, loaned out, or conceded.”

Frustrated that one of the sculptures should appear in St Petersburg, he said the move was “an affront to the Greek people”. The Parthenon and its marbles have been looted. The sculptures are priceless.”

The British Museum said the State Hermitage Museum had contacted them over the possible loan of one of the marbles in September last year.

It was the first time anyone had asked, a spokeswoman for the British Museum said, adding: “The trustees have always made it clear they are willing to lend.” She also revealed that the museum was in discussions with other institutions over potential further loans.

The statue – depicting the river god Ilissos – will be on display in the Hermitage from today until 18 January.

It was quietly removed from public view in November, with a note saying it was being made ready for display. It left the museum’s premises on Monday and secretly arrived in Russia the following day, with news finally breaking yesterday morning. It has been lent to help celebrate the 250th anniversary of the Hermitage. Neil MacGregor, the director of the British Museum who was in St Petersburg yesterday, said: “It is a very big moment.”

The British Museum houses about 30 per cent of the original Parthenon sculptures, which are 2,500 years old. The Louvre in Paris and the Vatican also have fragments.

The museum has always maintained that the objects – removed during the Ottoman occupation of Greece – were purchased legally and that the museum is the best place to display them. “The purpose of the British Museum is to present the world to the world,” it claims.

But Mr Samaras said yesterday: “The existence of the new Acropolis museum [has] invalidated the other British argument that there was no appropriate space for exhibiting the sculptures.”

Some also questioned the arrangement of a loan to a Russian institution given the diplomatic tensions between London and Moscow.

But Mr MacGregor said: “It’s precisely because relations between the countries are difficult that this kind of loan is important and so does the Hermitage.” Speaking to BBC Radio 4’s Today programme, he added: “Both institutions believe it is precisely at moments like this that the museums have to keep speaking.”

As things stands, the marbles are unlikely to end up in Greece on even a temporary basis. The Greek government has ruled out asking for a loan, but should that policy be reversed the British Museum says it would need assurances the marbles would be returned.

The Hollywood actor George Clooney waded into the row earlier this year when he called for them to be returned to Greece. His wife, the British lawyer Amal Clooney, is part of the legal team advising the Greek government on a potential challenge to force the return of the marbles.